Process for the production of allyl acetate

ABSTRACT

A process for providing high space time yields in the acetoxylation of propylene involving the use of a catalyst consisting esssentially of palladium, potassium, bismuth, and a promoting amount of magnesium or a combination of magnesium and barium.

This application is a division of application Ser. No. 642,464, filed onAug. 20, 1984, now pending.

BACKGROUND

This invention relates to a process for the production of allyl acetate.More particularly the present invention relates to the production ofallyl acetate by the acetoxylation of propylene.

It is known that allyl acetate can be produced by reacting propylene,oxygen, and acetic acid over a palladium-containing catalyst. Numerousexamples of promoters for the catalyst are reported in the literature.One of the more effective types of catalysts are those comprisingpalladium, potassium, and bismuth supported on an inert support. Evenwith such catalysts the optimum conditions have been found to give onlyabout 5-10% conversion of the propylene, with no more than about 90%selectivity to allyl acetate for a space time yield of about 250-320grams of allyl acetate per liter of catalyst per hour.

Obviously, it would be desirable to have a process which provided stillbetter selectivity, conversion, or space time yield.

An object of the present invention is to provide an improved process forthe acetoxylation of propylene.

Still another object of the present invention is to provide acomposition of matter suitable for use as a acetoxylation catalyst.

SUMMARY OF THE INVENTION

In accordance with the present invention a process is provided forpreparing allyl acetate comprising reacting propylene, acetic acid, andoxygen under suitable reaction conditions in the presence of a catalystconsisting essentially of palladium, potassium, bismuth, and a promotingamount of magnesium and optionally barium, deposited on a support.

DETAILED DESCRIPTION

The catalysts of the present invention are prepared by depositing theactive components on the support and subsequently drying the resultingcomposite.

The supports include those typically used for acetoxylation catalysts.Examples include silica, aluminum oxide, aluminum silicates, silicates,titanium oxide, zirconium oxide, titanates, pumice silicium carbide,silica gel, spinels, and mixtures thereof. It is preferred to usesupports having a high chemical resistance to water and acetic acid suchas silica for example. Especially suitable are silica having a nitrogensurface area in the range of 40 to 350 m² /g.

The palladium of the catalyst can be in the form of free palladium metalor in the form of a compound of palladium which is preferably free ofhalogens, sulfur, and nitrogen. Examples of such compounds includepalladium acetate, palladium propionate, palladium acetylacetonate orpalladium hydroxide. It is currently preferred to employ a palladiumcarboxylate, especially palladium acetate.

The other active components are applied in the form of acetates orcompounds which will be converted to acetate either during the catalystprep or during the acetoxylation process. Examples include the formates,propionates, hydroxides, carbonates, phosphates, borates, citrates,tartrates, or lactates of the other active metal components.

The catalyst can be prepared in many different ways, for example acompound of the metal can be dissolved in a solvent, the supportimpregnated with the resulting solution and then dried. It is alsopossible, however, to impregnate the support successively with thecomponents which can then be converted, if required, by an intermediatetreatment, such as calcination, or chemical reactions such as forexample treatment with solutions of an alkali metal hydroxide, alkalimetal carbonate or a reducing agent. The catalysts can be prepared froma compound containing sulfur, nitrogen or halogen, which compound isthen converted on the support into an insoluble compound which issubstantially free of sulfur, nitrogen or halogen.

The currently preferred technique of preparing the catalyst, however,involves dissolving the metal components in glacial acetic acid, thenimpregnating the support, and then drying the resulting solid.

The amount of palladium employed on the catalyst can vary from about 1to about 3 weight percent, most preferably about 1 to about 2 weightpercent based on the weight of the support.

The amount of potassium can vary from about 3 to about 7 weight percent,more preferably about 4 to about 5 weight percent based on the weight ofthe support.

The amount of bismuth can vary from about 1 to about 3 weight percent,more preferably about 1.5 to 2.5 weight percent based on the weight ofthe support.

The magnesium, and barium, when employed, should be present in an amountsufficient to result in an improved selectivity or space time yield overa catalyst containing only Pd, Bi, and K. The specific amount neededwill vary somewhat depending upon the amounts of Pd, Bi and K in thecatalyst. Typically, the amount of magnesium will be at least about 0.2weight percent and less than 0.5 weight percent, most preferably about0.3 weight percent based on the weight of the support. The amount ofbarium will typically be at least 1 weight percent and no greater than 2weight percent, most preferably about 1 weight percent.

In carrying out the acetoxylation propylene, oxygen, and acetic acid inthe gaseous phase are contacted with the inventive catalyst at atemperature in the range of about 100° C. to about 250° C. and pressuresof 1 to 25 absolute atmospheres. It is advantageous to use aconcentration ratio which ensures that the reaction mixture does notattain the known explosion limits. The simplest way to do this is tokeep the concentration of oxygen low, e.g. about 3 to 8% of the totalfeed employed. Generally, the non-reacted products may be recycled in acyclic process.

It has been typically noted that the preferred results are obtained ifthe reaction is carried out at a temperature in the range of about 160°C. to about 180° C. and a pressure of about 42 to 120 psig, morepreferably 75 to 100 psig.

The reaction mixture may also contain diluent gas which does notadversely affect the reaction such as nitrogen, carbon dioxide, andsaturated hydrocarbons.

It is also within the scope of the invention to include water along withthe reactants supplied to the catalyst. In fact it has been found thatin many cases the inclusion of certain amounts of water with thereactants can result in further improvements in the conversion and insome cases the selectivity as well. Accordingly, in order to obtain thebest space time yield it is recommended that water be included with thereactants. The amount of water employed is generally in the range ofabout 10 to about 30 weight percent of the acetic acid, more preferablyabout 15 to 25 weight percent.

The rate of contact of reactants and catalyst can vary over a wide rangedepending upon the conditions employed. Typically, however, the aceticacid would be supplied at a rate of about 0.4 to about 1.2 volumes pervolume of catalyst per hour, more preferably about 0.7 to 0.9. Thepropylene would typically be supplied at a rate sufficient to provideabout 0.5 to about 2 grams of propylene per milliliter of catalyst perhour, more preferably about 0.7 to about 1.5 g/ml/hr.

A further understanding of the present invention and the advantages thatit provides will be provided by the following examples.

In the following examples the general procedure involved in preparingthe catalysts involved dissolving the metal salts in glacial aceticacid, immersing the support with the solution, soaking the support for 2hours. Then the liquid was removed using a rotary evaporator and thecatalyst dried by heating for 3 hours in a convection oven at 120° C.The support employed was a silica sold by Davison Chemical Co. as highsurface area silica number G-59 of 8-12 mesh. The acetoxylations werecarried out in a metal pipe 1/2" by 20" packed with 50 ml of catalyst.Heat was supplied via a steam jacked around the pipe. After oxidationwas established it was continued for about 3 hours and then a totalsample of the reactor effluent was taken for 2 hours. The products wereanalyzed on a 5880 Hewlett Packard gas chromatograph using a 1/8"×36"Poropak Q column. The quantities of oxidation products were used tocalculate conversion, selectivity and catalyst productivity using thefollowing formulas: ##EQU1##

EXAMPLE I

A series of catalysts were prepared using the acetates of Pd, K, and Bito evaluate the effect of varying the levels of those metals. Theresults of the employment of those catalysts are summarized in Table I.

                  TABLE I                                                         ______________________________________                                        EFFECT OF CATALYST COMPONENT CONCENTRA-                                       TIONS ON REACTION RESULTS                                                           Pro-                      Selec-                                                                              Con-                                    Run   pylene,  Pd,.sup.(2)                                                                          K.sup.(2)                                                                          Bi,.sup.(2)                                                                        tivity,                                                                             version,                                                                             STY,                             No..sup.(1)                                                                         g/l/hr   %      %    %    %     %      g/l/hr                           ______________________________________                                        1     75       1.2    4.8  2    85.4  7.0    213                              2     75       1.5    4.8  2    90.3  7.8    250                              3     75       2.25   4.8  2    88.0  9.5    300                              4     75       1.5    3.2  2    82.7  9.6    283                              5     75       1.5    4.8  2    90.3  7.8    250                              6     75       1.5    6.4  2    88.4  5.3    167                              7     75       1.5    4.8  1    69.0  8.5    210                              8     75       1.5    4.8  2    90.3  7.8    250                              9     75       1.5    4.8  3    61.1  6.9    151                              ______________________________________                                         FOOTNOTES:                                                                    .sup.(1) Reaction Conditions: 42 ml/hr acetic acid, 4.5 l/hr O.sub.2, 75      psig pressure, 180° C.                                                 .sup.(2) Weight percent based on the support                             

The data of runs 1-3 shows that as the level of palladium rose, so didthe propylene conversion and productivity. However, optimum selectivityappeared to occur at about 1.5 wt % Pd. The data of runs 4-6 shows thatthe conversion and STY declined as the amount of potassium was increasedfrom 3 wt %. However, optimum selectivity was observed with 4.8 wt %potassium. Runs 7-8 employ varying levels of bismuth. The runs indicatethat the best results are obtained with the amount of bismuth is in therange of 1 to 3 weight percent.

EXAMPLE II

Another series of catalysts were prepared using yet other metals of thetype which have been suggested for use as promoters for Pd-basedacetoxylation catalysts. The results obtained of those catalysts issummarized in Table II.

                                      TABLE II                                    __________________________________________________________________________    STUDY OF THE EFFECTS OF METAL ADDITION TO THE Pd--K--Bi                       OXIDATION CATALYST                                                                  Pd,.sup.(2)                                                                      KOAc,.sup.(2)                                                                      Bi,.sup.(2)                                                                      Other,.sup.(3)                                                                      Selectivity                                                                         Conversion,                                                                          STY                                       Run No..sup.(1)                                                                     %  %    %  %     %     %      g/l/hr                                    __________________________________________________________________________    10    1.5                                                                              4.8  2  --    90.9  10.0   323                                       11    1.5                                                                              4.8  2  2% Cd 65.4  7.2    168                                       12    1.5                                                                              4.8  2  0.4% RE.sup.(4)                                                                     82.0  9.2    268                                       13    1.5                                                                              4.8  2  1.5% Sb                                                                             64.0  8.9    203                                       14    1.5                                                                              4.8  2  2% Pb 90.7  7.2    235                                       15    1.5                                                                              4.8  2  2% Mg 92.6  7.2    239                                       16    1.5                                                                              4.8  2  2% Ca 81.8  6.7    196                                       17    1.5                                                                              4.8  2  2% Ba 83.7  7.4    220                                       18    1.5                                                                              4.8  2  2% Sr 83.0  10.7   316                                       19    1.5                                                                              4.8  2  2% Cs 85.1  11.8   360                                       __________________________________________________________________________     FOOTNOTES:                                                                    .sup.(1) Reaction Conditions: 4.5 l/hr O.sub.2, 42 ml/hr acetic acid,         180° C., propylene 75 g/hr                                             .sup.(2) Weight percent based on support                                      .sup. (3) Weight percent metal acetate added to support                       .sup.(4) A mixture of rare earth metal acetates                          

The run using magnesium stands out in that it alone gave betterselectivity than the control catalyst of run 10.

EXAMPLE III

Still another series of catalysts were prepared employing magnesium as acatalyst additive. The results of the use of those catalysts issummarized in Table III. (Runs 10 and 7 are included in the Table forease of comparison.)

                                      TABLE III                                   __________________________________________________________________________    EFFECT OF MAGNESIUM LEVELS ON BASIC Pd--K--Bi CATALYST                              Temp.,                                                                            Propylene,                                                                          Pd,.sup.(2)                                                                      K,.sup.(2)                                                                       Bi,.sup.(2)                                                                      Mg,.sup.(2)                                                                       Selectivity,                                                                        Conversion,                                                                          STY,                                Run No..sup.(1)                                                                     C   g/hr  %  %  %  %   %     %      g/l/hr                              __________________________________________________________________________    10    180 75    1.5                                                                              4.8                                                                              2  --  90.9  10.0   323                                 20    180 75    1.5                                                                              4.8                                                                              -- .34 79.9  7.3    207                                 21    180 75    1.5                                                                              4.8                                                                              2  .17 86.8  8.5    262                                  7    180 75    1.5                                                                              4.8                                                                              1  --  69.0  8.5    210                                 22    180 75    1.5                                                                              4.8                                                                              1  .34 88.0  9.9    310                                 23    180 75    1.5                                                                              4.8                                                                              1  .17 62.7  3.6     81                                 24    180 75    1.5                                                                              4.8                                                                              2  .51 88.1  7.1    222                                 25    180 75    1.5                                                                              4.8                                                                              2  .34 92.6  7.2    239                                 26    180 35    1.5                                                                              4.8                                                                              2  .34 93.6  14.6   227                                 27    180 100   1.5                                                                              4.8                                                                              2  .34 94.4  4.0    183                                 28    170 35    1.5                                                                              4.8                                                                              2  .34 95.6  10.1   161                                 __________________________________________________________________________     FOOTNOTES:                                                                    .sup.(1) Reaction Conditions: 42 ml/hr acetic acid, 4.5 l/hr O.sub.2.         .sup.(2) Weight percent based on the support.                            

Run 20 involved the use of a catalyst containing Mg but not Bi. Theconversion and selectivity were both inferior to comparable inventivecatalysts. A comparison of runs 10, 21, 23, and 24 indicates that betterresults would be obtained if the Mg level was at least about 0.2 wt %and less than about 0.5 wt %. A comparison of runs 7, 22, and 23 alsoreveals that a Mg level of at least about 0.2 wt % would be preferred.The best results were obtained using a low propylene rate (35 g/hr) togive high conversion and a reduced temperature (170° C.) to improveselectivity.

EXAMPLE IV

Still another series of catalysts were prepared to determine if amaterial could be found which would promote even the Pd/K/Bi/Mgcatalyst. A summary of the results is provided in Table IV.

                                      TABLE IV                                    __________________________________________________________________________    SUMMARY OF THE EFFECTS OF ADDITION OF Ba OR Ca TO THE Pd--K--Bi--Mg           CATALYST                                                                      Run                                                                              Temp.,                                                                            Propylene,                                                                          Pd,.sup.2                                                                        KOAc,.sup.2                                                                        Bi,.sup.2                                                                        Promoter,.sup.3                                                                     Promoter,.sup.3                                                                     Selectivity,                                                                        Conversion,                                                                          STY,                         No..sup.1                                                                        C   g/hr  %  %    %  1     2     %     %      g/l/hr                       __________________________________________________________________________    10 180 75    1.5                                                                              4.8  2  --    --   90.9   10.0   323                          15 180 75    1.5                                                                              4.8  2  2% Mg --   92.6   7.2    239                          29 180 75    1.5                                                                              4.8  2  2% Mg 2% Ca                                                                              78.4   5.2    140                          30 180 75    1.5                                                                              4.8  2  2% Mg 2% Ba                                                                              93.6   10.3   343                          31 180 75    1.5                                                                              4.8  2  2% Mg 4% Ba                                                                              87.3   5.7    178                          32 180 75    1.5                                                                              4.8  2  --    2% Ba                                                                              83.7   7.4    220                          __________________________________________________________________________     FOOTNOTES:                                                                    .sup.1 Reaction Conditions: 42 ml/hr acetic acid, 4.5 l/hr O.sub.2            .sup.2 Weight percent based on support                                        .sup.3 Weight percent metal acetate added to support                     

Run 29 shows that calcium was ineffective in providing additionalimprovement. Run 30 shows that about 1.1 weight percent barium based onthe support provided an improvement in both conversion and selectivity.Run 31 shows that if the amount of barium added is too great theimprovement is not obtained. Run 32 shows that the barium used withoutmagnesium is not as effective as magnesium used without the barium.

EXAMPLE V

Another series of runs were made to determine the effect thatincorporating water in the feed would have on the inventive catalysts.The results are summarized in Table V.

                                      TABLE V                                     __________________________________________________________________________    EFFECT OF H.sub.2 O ADDITION ON PROPYLENE OXIDATION                           Run                                                                              Temp.,                                                                            Press.,                                                                           Propylene,                                                                          Pd,.sup.2                                                                        K,.sup.3                                                                         Bi,.sup.2                                                                        Mg,.sup.2                                                                        H.sub.2 O,.sup.3                                                                  Selectivity,                                                                        Conversion,                                                                          STY,                            No..sup.1                                                                        C   psig                                                                              g/hr  %  %  %  %  %   %     %      g/l/hr                          __________________________________________________________________________    33 180 75  75    1.5                                                                              4.8                                                                              -- -- --  61.0  8.4    184                             34 180 75  75    1.5                                                                              4.8                                                                              -- -- 20  89.0  5.4    175                             35 160 75  35    1.5                                                                              4.8                                                                              2  .34                                                                              --  88.1  7.3    106                             36 160 75  35    1.5                                                                              4.8                                                                              2  .34                                                                              20  91.8  11.9   181                             37 160 75  75    1.5                                                                              4.8                                                                              2  .34                                                                              20  97.7  9.1    316                             38 160 75  75    1.5                                                                              4.8                                                                              2  .34                                                                              10  75.7  10.7   289                             39 160 75  75    1.5                                                                              4.8                                                                              2  .34                                                                              30  34.2  9.8     56                             __________________________________________________________________________     FOOTNOTES:                                                                    .sup.1 Reaction Conditions: 42 ml/hr solvent, 4.5 l/hr O.sub.2                .sup.2 Weight percent based on support                                         .sup.3 Weight percent H.sub.2 O based on acetic acid                    

Run 34 demonstrates that the addition of water to a Pd/K catalystincreases selectivity but lowers conversion so that the space time yieldis actually lower when the water is employed. In contrast runs 36 and 37show that when water is employed in the feed using the inventivecatalyst both selectivity and conversion are improved. Runs 38 and 39shows that there is an optimum level of water somewhere between 10 and30 weight percent, based on the acetic acid.

What is claimed is:
 1. A process for preparing allyl acetate comprisingreacting propylene, acetic acid, and oxygen under suitable reactionconditions in the presence of a catalyst consisting essentially ofmetals on a support, said metals consisting essentially of palladium,potassium, bismuth, and a promoting amount of magnesium or a combinationof magnesium and barium.
 2. A process according to claim 1 wherein thecatalyst contains 1 to 3 weight percent palladium, 3 to 7 weight percentpotassium, and 1 to 3 weight percent bismuth, said weight percentagesbeing based on the support.
 3. A process according to claim 2 whereinthe magnesium is at least about 0.2 weight percent and less than 0.5weight percent based on the weight of the support.
 4. A processaccording to claim 2 wherein said catalyst also contains barium and thebarium is at least 1 weight percent and no greater than 2 weight percentbased on the support.
 5. A process according to claim 3 wherein saidcatalyst consists essentially of palladium, potassium, bismuth,magnesium, and support.
 6. A process according to claim 5 wherein saidsupport is silica.
 7. A process according to claim 6 wherein saidcatalyst contains about 1.5 weight percent palladium, about 5 weightpercent potassium, about 2.0 weight percent bismuth, and about 0.3weight percent magnesium based on the weight of the support.
 8. Aprocess according to claim 7 wherein said catalyst is prepared byimpregnating said silica support with acetates of the metals and thendrying the catalysts.
 9. A process according to claim 8 wherein thereaction is carried out at a temperature in the range of 100° C. to 250°C. and a pressure of 42 to 120 psig.
 10. A process according to claim 9wherein the feed rate of acetic acid is in the range of about 0.4 toabout 1.2 volumes per volume of catalyst per hour and the feed rate ofthe propylene is in the range of about 0.5 to about 2 grams permilliliter of catalyst per hour.
 11. A process according to claim 4wherein said support is silica.
 12. A process according to claim 11wherein said catalyst contains about 1.5 weight percent palladium, about5 weight percent potassium, about 2.0 weight percent bismuth, and about0.3 weight percent magnesium based on the weight of the support.
 13. Aprocess according to claim 12 wherein said catalyst is prepared byimpregnating said silica support with acetates of the metals and thendrying the catalyst.
 14. A process according to claim 13 wherein thereaction is carried out at a temperature in the range of 100° C. to 250°C. and a pressure of 42 to 120 psig.
 15. A process according to claim 14wherein the feed rate of acetic acid is in the range of about 0.4 toabout 1.2 volumes per volume of catalyst per hour and the feed rate ofthe propylene is in the range of about 0.5 to about 2 grams permilliliter of catalyst per hour.
 16. A process according to claim 1wherein water is included in the reaction in an amount in the range ofabout 10 to about 30 weight percent based on the acetic acid.
 17. Aprocess according to claim 6 wherein water is included in the reactionin an amount in the range of about 10 to about 30 weight percent basedon the acetic acid.
 18. A process according to claim 10 wherein water isincluded in the reaction in an amount in the range of about 10 to about30 weight percent based on the acetic acid.
 19. A process according toclaim 11 wherein water is included in the reaction in an amount in therange of about 10 to about 30 weight percent based on the acetic acid.20. A process according to claim 15 wherein water is included in thereaction in an amount in the range of about 10 to about 30 weightpercent based on the acetic acid.